Products made from or incorporating plastic are used in almost any work place or home environment. Generally, the plastics that are used to create these products are formed from virgin plastic materials. That is, the plastics are produced from petroleum and are not made from existing plastic materials. Once the products have outlived their useful lives, they are generally sent to waste disposal or a recycling plant.
Recycling plastic has a variety of benefits over creating virgin plastic from petroleum. Generally, less energy is required to manufacture an article from recycled plastic materials derived from post-consumer and post-industrial waste materials and plastic scrap (collectively referred to in this specification as “waste plastic material”), than from the comparable virgin plastic. Recycling plastic materials obviates the need for disposing of the plastic materials or product. Further, less of the earth's limited resources, such as petroleum and polymers, are used to form virgin plastic materials.
When plastic materials are sent to be recycled, the feed streams rich in one or more plastic materials may be separated into multiple product and byproduct streams. Generally, the recycling processes can be applied to a variety of plastics-rich streams derived from post-industrial and post-consumer sources. These streams may include, for example, plastics from office automation equipment (printers, computers, copiers, etc.), white goods (refrigerators, washing machines, etc.), consumer electronics (televisions, video cassette recorders, stereos, etc.), small domestic appliances (coffee makers, electric kettles, rice cookers, etc.), automotive shredder residue (ASR, the mixed materials remaining after most of the metals have been sorted from shredded automobiles and other metal-rich products “shredded” by metal recyclers), electronics shredder residue (ESR, the mixed materials remaining after most of the metals have been sorted from electronics “shredded” by metal recyclers), packaging waste, household waste, building waste and industrial molding and extrusion scrap.
Different types of plastic parts are often processed into shredded plastic-rich streams. The variety of parts can vary from a single type of part from a single manufacturer up to multiple families of part types. Many variations exist, depending on at least the nature of the shredding operation. Plastics from more than one source of durable goods may be included in the mix of materials fed to a plastics recycling plant. This means that a very broad range of plastics may be included in the feed mixture. Some of the prevalent polymer types in the waste plastic materials derived from the recycling of end-of-life durable goods are acrylonitrile-butadiene-styrene (ABS), high impact polystyrene (HIPS), polypropylene (PP), polyethylene (PE), polycarbonate (PC), and blends of PC with ABS (PC/ABS), polyamides (PA), polymethyl methacrylate (PMMA), polyvinyl chloride (PCV), polyether ether ketone (PEEK), polysulfone (PSU), polyoxymethylene (POM) and others. In some cases, the polymer pieces contain flame retardants or fillers.
Mixtures of recycled plastic materials can also contain rubber, wood, thermosets and other non-plastic materials.
In order to create product streams suitable for the widest range of applications, it is desirable to purify the flakes such that they contain almost entirely one type of plastic and almost no non-plastic materials.
In the following, methods are described for separating the plastic flakes into streams that are suitable for re-use.